碳纤维强度的Weibull分析

碳纤维属于脆性材料。抗拉强度随着测试样品长度的增加而降低,这是缺陷控制强度的主要实验依据,对于同样长度的测试样品,强度值的分散性非常大,这表明缺陷在碳纤维表面和内部是随机分布。碳纤维经气相氧化后,抗拉强度可得到提高,这归因于表面裂纹的消除,或因氧化刻蚀而使裂纹尖端钝化。碳纤维强度的统计性质可用Weibull统计理论来分析。Weibull模数m可作为裂纹频率分布因子。     

缺陷是碳纤维的致命伤

着重论述了缺陷产生的原因及其对碳纤维抗拉强度的影响。碳纤维属于脆性材料,抗拉强度受控于各类缺陷;缺陷是碳纤维的致命伤。抗拉强度与缺陷之间的关系遵循格拉菲斯微裂纹理论;缺陷随机分布,服从最弱连接理论;缺陷愈小和愈少,抗拉强度愈高、CV值愈小。指出:提高碳纤维抗拉强度的基本思路是控制各类缺陷的产生,减小缺陷尺寸,减少缺陷数目;提高碳纤维力学性能的治本措施就是在于消除各类缺陷。     

用SEM研究PAN原丝的表面缺陷

有机聚丙烯腈纤维（PANF）经过一系列高温热处理（HTT）转化为无机碳纤维（CF），CF属于脆性材料，其抗拉强度受控于各类缺陷，它的缺陷大致可分为两大类，一类是先天性缺陷，即由原丝引入，另一类是后天性缺陷，在后处理过程中引入，本文主要是用扫描电子显微镜（SEM）研究PAN原丝的表面缺陷。     

单向碳纤维复合材料微观形貌与性能相关性研究

利用金相显微镜、电子探针、扫描电镜对不同基体的单向碳纤维复合材料截面、界面进行了观察比较。结果表明：相同工艺条件下制备的几种不同基体碳纤维复合材料中，环氧树脂基碳纤维复合材料缺陷多，但纤维与基体的界面结合强，材料抗拉强度高；酚醛树脂基碳纤维复合材料与乙烯基酯碳纤维复合材料缺陷少，但界面结合差，材料抗拉强度低；材料界面结合状态与工艺参数有关。改性酚醛树脂、探索合理的生产工艺参数对改善界面结合状态，提高材料综合机械性能具有重要意义。     

增材制造连续碳纤维增强金属基复合材料性能

采用增材制造工艺方法进行具有高比强度、密度小等优良性能连续碳纤维增强金属基复合材料的直接制备。研究了连续碳纤维表面改性、路径搭接率、打印喷头温度、基板温度、打印速度等过程处理方法及工艺参数对所制备金属基复合材料抗拉强度的影响。研究结果表明,对连续碳纤维原材料实施表面改性处理,可以实现制备过程中熔融金属基体与连续碳纤维之间的良好浸润复合,以提高复合材料的抗拉强度;增大路径搭接率,可以有效提高增材制造复合材料内部纤维的体积占比,从而增大其抗拉强度;升高打印喷头温度、基板温度、打印速度,可以减小熔融金属表面张力,提高其流动性,并有利于沉积层间实现良好重熔,从而有效避免在已沉积层表面裂纹处和路径搭接区凹坑处形成气孔缺陷,进一步提升复合材料的抗拉强度。     

利用扫描电子显微镜研究聚丙烯腈基碳纤维的形态结构

采用扫描电子显微镜(SEM)研究了聚丙烯腈(PAN)基原丝及其碳纤维的缺陷和表面沟槽等形态结构,并分析了表面处理后碳纤维与树脂基体的结合状态.结果显示:SEM可以直观地观察到PAN原丝及其碳纤维的表面及内部缺陷,这些缺陷主要遗传自原丝;经表面处理后,碳纤维与树脂基体间结合程度和强度显著提高.     

纤维表面处理对复合材料力学性能的影响

本文研究了碳纤维表面处理方法对纤维-基体界面剪切强度的影响．研究结果表明，相对于未进行表面处詈的碳纤维-所采用的胺基化处理和偶联剂处理两种表面处理方法都能够提高碳纤维界面的剪切强度，从而提高复合材料整体的抗拉强度和弹性模量。并且偶联剂处理方法具有更好的工艺性．     

高性能石墨纤维

1 碳纤维的分类碳纤维大致可分为通用型、高强型、高模型、高强高模型四大类。通用型碳纤维是指抗拉强度在 0.6－1.2GPa，抗拉模量 30－40GPa 左右，技术性能要求不高（相对于高性能碳纤维而言），但价格要求便宜，以便广泛用于民用产品；高性能碳纤维的抗拉强度一般在 3.0GPa以上，各牌号指标也不相同，但抗拉模量要求在 200GPa 以上，主要用于结构承力件。高模量型碳纤维则对抗拉模量要求较高，一般在 300GPa 以上，但对抗拉强度相对较低，主要用于要求形态稳定的部件；高强高模型碳纤维对抗拉强度和抗拉模量均要求很高，以适应特殊用…     

硝酸处理对碳纤维性能的影响

探讨了国产碳纤维表面硝酸处理及其对性能的影响。试验结果表明,碳纤维经65％浓硝酸表面处理后,其纵向抗拉强度有所提高。并用正交法选出了碳纤维表面硝酸处理的较佳工艺制度。     

提高碳纤维强度的理论基础及其技术途径

碳纤维属于脆性材料,它的抗拉强度受控于各类缺陷,基本遵循Griffith经典理论和韦氏（Weibull)统计规律,如何减少缺陷尺寸,减少缺陷数目是当今提高其拉强度的主要技术途径和研究热点。     

Tensile strength and its variation of PAN‐based carbon fibers. III. Weak‐link analysis

Both the strength and its variance of carbon fibers depend on the worst flaw that exists in the fiber, or more exactly speaking, on the structure of the “fiber weak link” (FWL). To better understand the strength–structure relationship, the fracture‐ends morphologies were examined by the scanning electron microscope (SEM). The weak links of carbon fibers were divided into three groups according to its tensile strength, and the effect of the carbon FWLs on the strength variance was also discussed. The observation by SEM, the analysis on fiber tensile properties, and the corresponding discussion of the two sorts of results indicate that both surface flaw and the incompact structure decrease the strength of carbon fiber and enlarge the strength variance of carbon fiber. The modulus seems to influence the strength of carbon fibers too. It is also confirmed that not only the size of the fracture mirror but also the ratio of the size of the mirror to the fracture surface area (not cross section area) is important for judging the strength of brittle fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The properties of dry-spun carbon nanotube fibers and their interfacial shear strength in an epoxy composite

Continuous fibers composed of carbon nanotubes have been adopted as reinforcements for polymeric composites. This paper presents several fundamental studies relevant to the mechanical behavior of CNT fibers, including fiber tensile behavior; in situ SEM observation of fiber deformation mechanisms; and fiber modulus, ultimate strength and fracture strain measurements. A modified Weibull strength distribution model that takes into account the flaw density variation with fiber diameter has been adopted for the statistical strength analysis. The interfacial shear strength between the carbon nanotube fiber and the epoxy matrix has been measured using fragmentation tests of single-fiber composites.     

High-temperature vapor deposition polymerization polyimide coating for elimination of surface nano-flaws in high-strength carbon fiber

The effect of polyimide coatings on the filament tensile strength of high-strength polyacrylonitrile-based carbon fiber was studied by using dip and high-temperature vapor deposition polymerization (VDP) coating processes. Unlike a VDP on a cold substrate, high-temperature VDP has the potential to directly synthesize and isotropically deposit a polyimide, from diamine and dihydride monomers without any by-products, on a substrate heated up to 200 °C. The average filament tensile strength of the flaw-sensitive carbon fiber improved with all the polyimide coatings used. Nevertheless, for the same monomers, the high-temperature VDP coating process was advantageous for high-efficiency surface flaw healing compared to the dip-coating process, resulting in a 25% increase in the average tensile strength of the carbon fiber. These results were evident not only for the carbon fibers without artificial nano-notches but also for those with artificial notches less than 30 nm in depth. Thus, we clearly showed the potential for the VDP polyimide coating to heal surface nano-flaws of the carbon fiber. The different infiltrations of the coating into nano-notches and its effect on the filament tensile properties were characterized, as well as discussing the impact of the VDP coating with an interlayer between the coating and the fiber.     

n-C7H16/CCl4热解处理对粘胶基碳纤维性能的影响

采用浸渍热解法,以n-C_7H_(16)/CCl_4为热解质,讨论浸渍液体积比、热解温度等对粘胶基碳纤维(RCF)拉伸性能的影响。结果表明,经热处理后纤维线密度降低,表面缺陷减少,当n-C_7H_(16)/CCl_4为2:3(体积比),热解温度900～1100℃时,碳纤维拉伸强度可提高17％。用韦氏统计理论对强度分布进行分析.证实经热解处理后,RCF强度分布更集中,均匀性更好。     

High strength carbon fibers from mesophase pitch

The tensile strengths of carbon fibers derived from mesophase pitch were determined as a function of gauge length in the range of 1.4–40 mm. Filaments were examined from a fiber apparently free from flaws, and the results were compared with data from filaments weakened by internal voids. Strengths with averages as high as 3.4 GPa were measured on 8 μm diameter filaments at a length of 1.4 mm. The tensile strength data were analyzed at each gauge length by using a two-parameter form of the Weibull equation. The shapes of the probability of failure versus strength plots, as well as the appearance of the histograms, showed that a secondary flaw population becomes significant at the longer filament lengths. Extrapolations based on the distributions of flaws which control the tensile strengths of the filaments at short test gauge lengths resulted in a predicted strength of 7 GPa at 0.1 mm length for both the void free and the flawed filaments. This average strength equals the best values reported for carbon filaments made from PAN.     

螺栓连接对二维机织物增强复合材料拉伸性能影响的实验研究

本文主要通过对单搭接螺栓连接的二维机织物增强层合板拉伸实验的分析，讨论了螺栓连接的物理参数，织物组织结构等因素对层合板强度，断裂方式等方面的影响。     

干喷湿纺聚丙烯腈原丝的预氧化和碳化工艺

分析了预氧化时间、温度对预氧丝密度的影响,研究了预氧丝密度和牵伸率以及张力、碳化升温速率与碳纤维抗拉强度之间的关系。试验结果证明:延长预氧化时间和提高预氧化温度,预氧丝密度提高;当预氧丝密度为1.355 g/cm3时,得到的碳纤维的强度最高;当预氧化牵伸率为0.93%时,对应的碳纤维强度为4.84 GPa;在300℃/min低温碳化升温速率和1000℃/min高温碳化升温速率下,可以得到高性能碳纤维。     

Producing high‐quality precursor polymer and fibers to achieve theoretical strength in carbon fibers: A review

The precursor fiber quality has a large impact on carbon fiber processing in terms of its performance, production yield, and cost. Polyacrylonitrile precursor fibers have been used commercially to produce strong carbon fibers with average tensile strength of 6.6 GPa. There is a scope to improve the average tensile strength of carbon fibers, since only 10% of their theoretical strength has been achieved thus far. Most attempts to increase the tensile strength of carbon fibers have been made during the conversion of precursor fiber to carbon fiber. This review highlights the potential opportunities to enhance the quality of the polyacrylonitrile‐based precursor fiber during polymer synthesis, spinning, and postspinning. These high‐quality precursor fibers can lead to new generation carbon fibers with improved tensile strength for high‐performance applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43963.     

碳纤维增强改性PVC拉伸强度的研究

研究了碳纤维增强改性PVC的拉伸强度,讨论了碳纤维及偶联剂用量对拉伸强度的影响.结果表明,在碳纤维的用量为11.7份,偶联剂的用量为0.083份时,PVC的拉伸强度达到最大,为90 MPa左右,此时材料的密度约为1.38 g/cm3.     

Effect of silane coupling agents on basalt fiber–epoxidized vegetable oil matrix composite materials analyzed by the single fiber fragmentation technique

The fiber–matrix interfacial shear strength (IFSS) of biobased epoxy composites reinforced with basalt fiber was investigated by the fragmentation method. Basalt fibers were modified with four different silanes, (3‐aminopropyl)trimethoxysilane, [3‐(2‐aminoethylamino)propyl]‐trimethoxysilane, trimethoxy[2‐(7‐oxabicyclo[4.1.0]hept‐3‐yl)ethyl]silane and (3‐glycidyloxypropyl)trimethoxysilane to improve the adhesion between the basalt fiber and the resin. The analysis of the fiber tensile strength results was performed in terms of statistical parameters. The tensile strength of silane‐treated basalt fiber is higher than the tensile strength of the untreated basalt fiber; this behavior may be due to flaw healing effect on the defected fiber surfaces. The IFSS results on the composites confirm that the interaction between the fiber modified with coupling agents and the bio‐based epoxy resin was much stronger than that with the untreated basalt fiber. POLYM. COMPOS., 36:1205–1212, 2015. © 2014 Society of Plastics Engineers